Proposal on LBB evaluation conditions for sodium cooled fast reactor pipes and effects of pipe parameters

Abstract

In the in-service inspection of sodium cooled fast reactors, an examination by continuous leak monitoring will be applied for components constituting sodium boundaries. The continuous leak monitoring examinations are premises in a LBB (leak before break) being established. In previous LBB evaluation, the axial crack of the elbow flank has been evaluated, because in the piping system of the fast reactor with high thermal expansion, high stress is generated in the elbows flank. However, the LBB evaluations for circumferential cracks are important in the point of continuous leak monitoring in the in-service inspection. In this study, the load conditions in the LBB assessments for circumferential cracks were examined and LBB characteristics of class 1 pipes of the prototype fast breeder reactor "Monju" were evaluated as an example. Additionally, in order to research the relationship between pipe condition and LBB, many pipes were evaluated with actual conditions. As results, following conclusions were obtained. It was demonstrated that LBB characteristics are established at class 1 pipes in “primary heat transport system” and “cooling system for maintenance” of “Monju”. LBB characteristics are correlated with pipe diameter and thickness.

Keywords

• sodium-cooled fast reactor
• leak before break
• crack
• unstable fracture
• leak rate
• penetrated crack length
• in-service inspection